Prepress color proofing is a procedure that is used by the printing industry for creating representative images of printed material to check for color balance and other important image quality control parameters, without the high cost and time that is required to actually produce printing plates and set up a printing press to produce an example of an intended image. These intended images may require several corrections and may be reproduced several times to satisfy or meet the requirements of the customers, resulting in a large loss of profits and ultimately higher costs to the customer.
Generally speaking, color proofs sometimes called "off press" proofs or prepress proofs, are one of three types: namely (1) a color overlay that employs an image on a separate base for each color; (2) a single integral sheet process in which the separate color images are transferred by lamination onto a single base; and (3) a digital method in which the images are produced directly onto or transferred by lamination onto a single base from digital data.
In one typical process for a prepress color proofing system used in the printing industry, a multicolor original is separated into individual transparencies, called color separations, the three subtractive primaries and black. Typically a color scanner is used to create the color separations and in some instances more than four color separations are used. The color separations are then used to create a color proof sometimes called an "off press" proof or prepress proof as described above.
A KODAK Color Proofing Laminator can be used to bond lamination sheets to receiver stock as a part of a color proofing system. The lamination sheets include a carrier and a layer of material to be applied to the receiver stock, which, in the case of the Kodak Color Proofing Laminator, is a color donor. A lamination sheet is laid upon the receiver stock with the color donor side sandwiched between the carrier and the receiver stock forming a lamination sandwich.
FIG. 1 shows a laminator 12 as described in U.S. Pat. No. 5,478,434. As shown in FIG. 1, a lamination sandwich 10 sits on an entrance table 20. A leading edge of lamination sandwich 10 is fed into a laminator 12 which includes an upper heated pressure roller and a lower heated pressure roller. Lamination sandwich 10 passes completely through the upper heated pressure roller and the lower heated pressure roller. Lamination sandwich 10 thereafter exits the upper heated pressure roller and the lower heated pressure roller and comes to rest on an exit table 14 undisturbed until the trailing edge is cool to the touch; whereupon the top-most carrier can be peeled away from receiver stock and from the transferred color donor. With the configuration of an upper heated pressure roller and a lower heated pressure roller as described above, the laminator is called a straight-through laminator. Further details of this type of lamination/de-lamination system can be found in the above. As an additional reference, U.S. Pat. No. 5,203,942 describes a lamination/delamination system as applied to a drum laminator.
While the above-described laminator works well for a few materials and in limited conditions, there are many conditions and materials that cannot be laminated successfully using the above-described laminator. One problem is the intended image shifting from one color to another such that the dots/image from one color to the next are not overlaid correctly causing a misregistration of the intended image rendering it unacceptable. Also damage to some media may occur in the form of speckles/freckles or creases commonly know as rivers or valleys.
The aforementioned problems are for the most part due to the heated pressure rollers and there application. The upper heated pressure roller and the lower heated pressure roller have hollow cores that are typically made of metal. The hollow portion of the core is for accepting a heating rod or lamp while a rubber layer or shell typically of silicone rubber is formed around the outside of the core. However, in some cases there may be no rubber layer or shell. Typically one of the heated pressure rollers will have a different durometer. Typically one heated pressure roller has a 50-60 SHORE A durometer and the other a 65-80 SHORE A durometer and in some cases they are the same durometer. When the upper heated pressure roller and the lower heated pressure roller are pressed together they form a nip or indentation which is typically 7-10 mm wide and varies considerably along the length of the heated pressure rollers at a pressure of 40-80 PSI. Within the nip formed by the upper heated pressure roller and the lower heated pressure roller, lateral shear stresses and overdrive conditions are formed. These lateral sheer stresses and overdrive conditions act upon the media being laminated together to cause the intended image to shift from one color to another color. These lateral sheer stresses and overdrive conditions can also cause a defect in the final lamination in the form of creases commonly known as a rivers or valley, as described above. These lateral sheer stresses and overdrive conditions can also cause image growth which can be different with each color, causing the intended image to misregister from one color to the next color or to be larger than the original image or printed image.
Further drawbacks with the above mentioned conventional lamination arrangement is the creation of speckles/freckles, flutes and ripples in the paper (especially due to humidity on a subsequent pass of the paper), as well as the lack of control of the paper prior to entering the nip portion between the pressure rollers. Also, the conventional arrangements do not provide for an adequate mechanism to hold the paper down after it leaves the nip portion and is cooling down.